The present invention relates generally to wood processing, and particularly to a feed mechanism and cutting arrangement for around the curve sawing.
As the use of second growth timber in lumber processing operations continues and the increased use of certain species of irregularly formed logs continues, the need grows for improved methods of recovery in the process of converting these raw materials into suitable lumber products. One area in which improved recovery may be obtained is by taking into account the sweep or curvature of the log in cutting the log into wood products. More particularly, if a curved or sweepy log is cut along its curve, then more wood product may be recovered from the log than would be possible in a more conventional process using straight cuts.
There are a number of patents which address the issue of around the curve sawing in order to improve recovery from sweepy logs or cants. In one approach, a curved linebar is used to guide a workpiece along a curved path and into a sawing device. The curved linebar is adjustable to match generally the curvature of the workpiece in the hope that by placing the exterior surface of the workpiece against the curved linebar and moving it along the linebar, it will move along an appropriate path into the cutting device to accomplish the desired around the curve cutting.
The prior method of improved product recovery by means of a curved linebar has proven useful in certain situations. More particularly, the use of a curved linebar is most efficient only where the curvature of the workpiece is generally well behaved. Most species of trees in the western portion of the United States have what will be referred to herein as "well behaved" curves. In particular, well behaved cants or logs have an exterior surface that lies substantially concentric to its overall curvature. In such cases, this exterior curved surface may be placed against a curved linebar with the linebar adjusted to provide a corresponding curvature and the desired improved recovery may be obtained.
Other species of trees, for example, Southern Yellow Pine, are not well behaved because of knot protrusions, swelled butts, S-crook, and sweep. Such tree species are not well suited for use with a curved linebar because the protrusions and irregularities of cants produced from these trees do not provide an exterior surface matching the general curvature of the cant and providing a suitable surface for placement against a curved linebar. The position of the cant against the linebar is critical with respect to the actual cut made. If a tapered cant has a large swelled butt, the main body of the cant in the butt area will be forced out away from the linebar while the other end of the cant will be located closer to the linebar. With such irregular positioning with respect to the curved linebar, the ideal first saw cut or opening face cannot be achieved and relatively lower lumber yields result. Thus, misalignment of the curvature of the cant relative to the curved linebar results in an inability to significantly improve recovery.
Swedish Patent No. 33,098 shows a sawing device having two feed roll assemblies, each with parallel upper and lower rollers for gripping a log therebetween. Each roll assembly can be pivoted so that the axes of rotation for each assembly lie at an angle and intersect at a point defining a curve along which the log is to travel in cutting the log. Each roll assembly is pivoted about a corresponding pivot point whereby the roll assembly axes of rotation may be selectively oriented in parallel relation or in relative angular relation for establishing a straight or a curved feed path. Because the rollers contact the crest of the log surface, the shape of the log itself when irregular or not well behaved will affect significantly the resulting curved feed path. Thus, for logs without well behaved curvature or irregular surfaces the resulting feed path is unpredictable and unacceptable in a high efficiency recovery system. The respective pivot points define a line parallel to a straight feed path of the cutting device. There appears to be no practical way to add additional roller assemblies in order to accommodate long work pieces. The disclosed method of pivoting roller assemblies to provide curved path feeding would permit relative angular positioning by pivoting of more than two roller assemblies to establish a common point of intersection for such roller assembly axes of rotation, but one end of each roller assembly remains fixed and in alignment with the other roller assemblies. This is believed to limit significantly the available curved feed paths for more than two roller assemblies. Furthermore, as the roller assemblies are pivoted to establish a curved feed path, the resulting curved feed path has no fixed relationship to the cutting device. In other words, each selected curved feed path is defined by the angular relation between the rollers with no portion of the feed path having a fixed position other than with reference to the roller assemblies which necessarily move to establish the curved feed path. This "floating" curved feed path would require, in a high efficiency recovery system, repositioning of the cutting device according to the position of each selected feed path.
Accordingly, it would be desirable to provide an around the curve sawing apparatus better adapted to handle, for example, irregularly shaped sweepy cants and allow for a large number of roller assemblies. The subject matter of the present invention provides such an apparatus and may be applied to improve recovery from irregularly shaped tree species.